The present invention relates to an electric controlling element for the power-setting element of an internal combustion engine in which the controlling element operates a power setting element such as a throttle valve, the controlling element including a drive device and a clutch having an electromagnet arranged between the drive device and the power-setting element and wherein, upon passage of current to said electromagnet, an armature is attracted against the force of a spring, the clutch being thereby closed.
Such known controlling elements are used in systems for regulating the speed of motor vehicles, the vehicle maintaining a preselected speed by automatic displacement of the power-setting element, for instance the throttle valve. Furthermore, such controlling elements can also be used to control the speed of the vehicle, the position of the gas pedal being transmitted electrically to the power-setting element (so-called E-gas systems).
In one known electric controlling element a drive device is provided which consists of an electric motor, a gearing and a spindle drive and moves a plunger magnet linearly. The plunger magnet cooperates with an armature plate which is connected, as clutch, via a pull cable to the throttle valve. In normal operation, the clutch which consists of the plunger magnet and the armature plate is closed, so that the linear movement produced by rotation of the spindle is transmitted to the pull cable and thus to the throttle valve. This movement takes place in opposition to the force of a return spring which seeks to pull the throttle valve into the idling position.
The clutch formed by the plunger magnet and the armature plate has the task of maintaining the force lock between the drive device and the throttle valve under normal operation but to disconnect rapidly the drive device from the throttle valve if the vehicle brake or clutch is actuated. For this purpose, the current is disconnected from the winding of the plunger magnet so that the return spring can move the throttle valve into its idling position. The clutch is furthermore opened in the event of an error in the control or regulating system or if, for instance, the operating voltage fails.
In the known controlling element, limit switches are provided which are actuated when the plunger magnet reaches its end positions. In this way, the drive device can be disconnected when the end positions are reached. In the known controlling element it may happen that when the clutch is open, the current is again connected through the winding of the plunger magnet and, upon a corresponding movement of the gas pedal or corresponding control by the speed governor system, the plunger magnet approaches the armature plate and attracts it, as a result of which the throttle valve is suddenly opened. This, in its turn, can lead to a dangerous situation.